Stabilized polyamide compositions

ABSTRACT

Heat stabilized synthetic polyamide compositions are prepared by incorporating therein a mixture of a phenolic antioxidant and metal hypophosphite. A typical embodiment includes polyamides which are stabilized with 1,2-bis(3-(3,5-di-t-butyl-4hydroxyphenyl)propionamido)ethane and sodium hypophosphite.

United States Patent 1 Klemchuk 1 Jan. 14, 1975 STABILIZED POLYAMIDE COMPOSITIONS [75] Inventor: Peter Klemchuk, Yorktown Heights,

[73] Assignee: Ciba-Geigy Corporation, Ardsley,

[22]Filed: 0667,1970 21 A 1.N6.; 95,912

[52] US. Cl, 260/45.8 N, 260/45.7 P,

260/45.75 R, 260/45.9 NC

51 Int. Cl oos 51/56, C08g 51/60 [58] Field of Search 260/45.7 P, 45.8 N, 45.9 R, 260/45.9 NC, 45.75 R

[56] References Cited I UNITED STATES PATENTS 2,510,777 6/1950 Gray 260/45.7 3,435,065 3/1969 Dexter et al. 260/473 3,493,633 2/1970 Lange 260/857 3,533,986 10/1970 Davy ..260/37 3,584,047 6/1971 Dexter et al.. 260/559 3,595,829 7/1971 Davy 260/45.8

FOREIGN PATENTS OR APPLICATIONS 812,262 5/1969 Canada OTHER PUBLICATIONS Def. Publ., T872,009, Keith et al.

Primary ExaminerDonald E. Czaja Assistant ExaminerR. A. White Attorney, Agent, or FirmNestor W. Shust [57] ABSTRACT 10 Claims, N0 Drawings STABILIZED POLYAMIDE COMPOSITIONS DETAILED DESCRIPTION This invention relates to synthetic polyamide compositions having improved oxidative stability. More specifically, it relates to a synthetic polyamide composition stabilized against oxidative and thermal deterio forming components. More particularly, are intended the class of polyamides known generally as nylons of which polyhexamethylene adipamide and polycapro- -lactam are familiar examples. Within this class are also included interpolyamides, that are obtained, for examp1e,'by the polycondensation of a mixture of hexamethylene diammoniumadipate with caprolactam.

' a known manner. Particularly suitable polyamides of 5 weight percent of a hindered phenolic compound having the formula:

A is selected from the group consisting of F Q F s i- H V H H H and This invention is useful for polyamides in all forms. Particularly preferred are those polyamides which may be obtained in fibrous form by melting, spinning the molten material and drawing the resultant filaments in our invention are those in which the polyamide is polyhexamethylene adipamide.

Th'e phenolic antioxidants and the hypophosphite compounds can be incorporated into the polyamide before, during or after the polycondensation step. Thus the phenolic antioxidant and the hypophosphite can be added to the polymer forming ingredients before the polycondensation step or during the polycondensation process and the reaction completed by heating. The phenolic antioxidant and the hypophosphite compound can also be added to the already formed polyamide by adding the phenolic antioxidant and hypophosphite mixture to the molten polyamide or alternatively they can be mixed with the solid polyamide or the solid polyamide in theformbf lumps, pellets, or chips may be coated with the ingredients and the polyamide then where mis a number from 2 to 8 and -(C,,,I-I is linear or cyclic; or r wherein R and R are as defined above and y is alkylene from I to 10 carbon atoms or C,.

H SC H Illustrative examples of lower alkyl groups which are represented by R and R are methyl, ethyl, propyl, isopropyl, t-butyl, pentyl and hexyl. The preferred groups are methyl and the branched alkyls such as tertiary butyl and isopropyl.

Illustrative examples of the metal from groups Ia, Ila and lIb which can be used as the metal hypophosphite are lithium, sodium, potassium, barium, magnesium, calcium, strontium and zinc. The transition metal manganese can also be used. The preferred metal hypophosphites are sodium hypophosphite and potassium hypophosphite and sodium hypophosphite is the most preferred. v

By synthetic polyamides is meant condensation polymers obtained by the polycondensation of amino carboxylic acids or of mixtures of diamin es' and dicarboxylic acids including interpolyamides obtained by the polycondensation of mixtures of different polyamide melted. The preferred embodiment for the incorpora tion during polymerization is the addition of the phenolic antioxidant and hypophosphite just prior to discharge of the polyamide after the polycondensation is completed with enough time allowed for uniform distribution vof the stabilizers throughout the melt.

Listed below are illustrative examples of the hindered phenolic derivatives of the general type. described which can be effectively employed with a metal hypophosphite to act as antioxidants for the purpose of the present invention:

l,6-bis[ 3-( 3 ,5-di-t-butyl-4-hydroxyphenyl)propionamido]-hexane, I 1 ,2-bis 3-( 3 ,5-di-t-butyl-4-hydroxyphenyl)pro pionamido]-ethane,

l ,4-bis[ 3-'( 3 ,S-di-t-butylhydroxyphenyl)propionamidomethyllcyclohexane, v

N,N'-bis[3-(3,5-di-t-butyl-4- hydroxyphenyl)propionyll-piperazine,

l,6-bis[ 3-( 3-methyl-4-hydroxy-5-t-butylphenyl)propionamido]-hexane, I l ,2-bis[ 3-( 3-methyl-4-hydroxy-5-t-butylphenyl )propionamidol-ethane, N,N'-bis[3,5-di-t-butyl-4-hydroxybenzyl]adipamide, Bis[N-( 3 ,5-di-t-butyl-4-hydroxybenzyl )propionamide1-sulfide, l,6-bis[ 3-( 3 ,5-dimethyl-4-hydroxyphenyl)propionamido1-hexane, l,6-bis[ 3-( 3 ,5-dimethyl-4-hydroxyphenyl )propionamido]-hexane, N,N'-bis( 3-methyl-4-hydroxy-5-t-butylbenzyl )adipamide. The hindered phenolic compounds of this invention,

having the formula I above, can be prepared via a number of conventional amidation procedures. Thus, an acid of the formula H 110 -CH CH -C-0H III wherein R and R are as defined above or an alkyl ester thereof and a polyamine are heated in an inert solvent with the generation of water or an alcohol. Alternatively, the polyamine and the acid halide of the compound of formula III, generally the acid chloride are allowed to react in an inert solvent, preferably in the presence of an organic or inorganic base which serves as an acid binding agent. The preparation of these compounds are explained in further detail in Belgian Pat.

' No. 726,092, issued June 27, I969.

The hindered phenolic compounds of formula II can be prepared through the condensation of an alkyl hydroxybenzyl alcohol anda dinitrile in the presence of an acid catalyst such as mineral acids. Generally the nitrile can be employed as the reaction medium as well as an inert organic solvent.

Alternatively, conventional methods of. amide preparation such as the reaction of an alkylhydroxybenzylamine and an alkanoic acid chloride are employed.

In the case wherein the group Y of formula II is CI-l CI-I -SCH CH these compounds are prepared by reacting an alkylhydroxybenzyl alcohol with acrylonitrile. The corresponding N- (alkylhydroxybenzyl)acrylamideis reacted with hydrogen sulfide which results in the coupling of two molecules of the acrylamide across the thio linkage, thus yielding a bis[N-(alkylhydroxybenzyl)propionamide]- sulfide. The preparation of the compounds of formula II are explained in more detail in Canadian Pat. No. 812,262, issued May 6, 1969.

The amount of metal hypophosphite incorporated into the polyamide may fall within the range of from 0.01 to 0.25 percent by weight of the polyamide but preferably within the range of from 0.05 to 0.15 weight percent. The amount of hindered phenolic compound iswithin the range of 0.01 to 5 percent by weight of the polyamide but is perferably withing the range of 0.1 to

2 weight percent. In the preferred embodiment of the- EXAMPLE 1 To 39.3 g (0.15 moles) of hexamethylenediammonium adipate were added 0.177 g (7.5 X 10 mole; 0.5 mole of hexamethylenediammonium diacetate as molecular weight control agent, 0.183 g (0.5% of theoretical nylon yield) of l,3-bis[3-(3,5-di-t-butylhydroxyphenyl)propionamido]ethane and 0.0366 g (0.1% of theoretical nylon yield) of sodium hypophosphite. The mixture was mixed thoroughly and added to a Pyrex polymer tube.

I The polymer tube was evacuated three times and filled with High Purity nitrogen each time. The polymer tube with a continuously maintained, slightly positive nitrogen pressure was placed in a methyl salicylate vapor bath at 222C. The nylon-6,6 salt melted with bubbling due to the liberation of water. After the bubbling ceased, a clear melt was obtained which solidified after 5-8 minutes. After 1 hour at 222C the polymer tube was transferred to an o-phenyl-phenol bath at 285C for 1 hour where the solid gradually remelted. The polymer tube was kept in the 285C vapor bath for an additional 1% hour while it was maintained under oil pump vacuum 1mm.). High purity nitrogen was then readmitted and the polymer tube was allowed to cool.

EXAMPLE 2 The plug of nylon-6,6 obtained in Example 1, was

ground in a Wiley mill at ambient temperature. About 2 g were heated in small glass Petri dish in a circulating air, rotary oven at C for 65 hours. The viscosity of a 1% sulfuric acid solution of aged and unaged polymer samples were determined at 25C. Stabilizer effectiveness was judged by the percent retention of specific viscosity and by color formation after oven aging. A polyamide containing no stabilizers was prepared and tested in a similar manner and their results with respect polyamide after oven aging.

TABLE I Specific Viscosity Polyamide Initial Retention vUnstabilized 1.64 57 Stabilized 1.62 96 EXAMPLE 3 Pellets (500 g) of unstabilized nylon-6,6 (Zytel 101,"

DuPont) were placed in a Kitchen Aid Mixer. With mixing a solution of 2.5 g (0.5%) of l,2-bis[3-(3,5-di-tbutyl-hydroxyphenyl)-priopionamide]ethane in 20 ml. of methylene chloride was added slowly. Sodium hypophosphite.(0.5 gm, 0.1%) was dissolved in 20 ml of water and added slowly with mixing to the nylon pellets after the antioxidant solution had been added and most of the methylene chloride had evaporated. The stabilized pellets were dried at 80C at lmm. for 4 hours.

The polyamide formulation was extruded at 600F. through a 1 inch die into a rod which was water cooled and chopped into pellets. A 54 inch Brabender extruder, equipped with a nylon screw, was used. The pellets were dried at 80 at lmm. for 4 hours.

The dried pellets were pressed into 5 X 5 X 0.005 inch films at 290 and 350 psi for 3 min. The mold was transferred quickly to a water-cooled press and maintained at 350 psi, for 2-3 mins.

Samples (2.2g) of compression molded nylon-6,6 films were aged in an air circulating, rotary oven at C for various time periods. Stabilizer performances were assessed by measurements of specific viscosity retention of oven aged samples in 11% formic acid solution. The time to 50% retention of the specific viscosity is reported in Table II below:

5 6 TABLE II EXAMPLE 5 Following the procedure of Example 1 but using fggijf f mm 0.5% of N,N'-bis[3,5-di-t-butyl-4-hydroxybenzylv 5. ]adipamide and 0.1% sodium hypophosphite, a stabig- None 200 lized polyamide composition is obtained which shows 384 considerably less color developemnt and substantially less weight loss after aging at 140C for 65 hours than a polyamide which is unstabilized. EXAMPLE 4 EXAMPLE 6 A two liter autoclave, equipped with a paddle stirrer, thermocouple well, bottom outlet valve, jacket for cir- Followmg the procedufe of Example but culating heat transfer fluid from an external heated resof -P ervoir, and valved outlets and inlets,.was used for the bfnylphenyl)prqplonamldolfllexane and Poms Polymerizations. slum hypophosphite, a stabilized polyamide composi- Nylon Salt, (300 Dow Badische) was dissolved tion is obtained which shows considerably less color dein 480 ml of warm distilled water. Hexamethylenediamvelopngem and Substantially less welght aftfir aging monium diacetate (2.69 g) was added as a molecular C for 65 hours than a polyamlde whlch unsta' weight control agent. The solution was added to the aublllzedtoclave, which was evacuated three times and filled Polyatmde composltlons are Prepared and l i with High purity nitrogen Nitrogen at v psi was left in a similar manner as above with the following stabi- On the reacmn The polymerization was Carried out lizer combinations and show the same superior results over a period of 4 hours with mixiumum temperature over the unstaPlllzed polysmldei and pressure reaching 280C and 250 psi respectively. N 9

The molten polymer issued froom the reactor bottom adpamlde 0 01% P F hypophosphlte outlet through a heated 3/16 inch circular die. The exbls[n'(3t5'dl'tbutyl'4hyflroxybenzyl)- trudate was passed through a nitrogen atmosphere into prglilonamldelsulfide and 01% Sodlum YP P a cold water bath. From the cold water bath the solid Sp e I v rod was passed into a pelletizer. The pellets were dried 'P 'Q l'4hyfjroxyphenyn' under oil pump Vacuum at 0 for 4 hours prop1onyl]p1perazine and 0.1% sodium hypopho- The antioxidants (3.45 g; 0.5%) and 0.69 g of sodium f hypophosphite (0.1%), were dispersed in 45g of water Wh Is clalmfed with the aid of Tritan Xl00, a dispersing agent. So- A synthetic polyamlde s.tablhzed dium hypophosphite was Soluble in water but the against oxldative and thermal deterioration which comoxidams were not Soluble. prises a polyamide having recurring amide groups as When added at the beginning of a polymerization the Integral parts of the P polymer chain from about stabilizer dispersion was charged to the autoclave along to weght Percent of a metal hypopho' with the nylon-6,6 salt solution. When added midway sphlte wherem Sald m l is Selected from the groups during a polymerization the stabilizer dispersion was g penodlc l g transferred to a small pressure vessel which was pres- 40 zz g z f $223329 a m ere p eno surized then to 400-500 psi with High Purity nitrogen. p g The pressure vessel was attached to the autoclave and O at the appropriate time, the dispersion was transferred IL by opening a valve between the autoclave and the pres- G surized storage vessel. When added as a dry mixture, i.e., 0.5% antioxidant and 0.1% sodium hypophosphite, wherein near the end of the polymerization the stabilizers were 1 and 2 are lower alkyl of from 1 to 6 carbon atoms added through a solid charging port while a stream of and nigrogen from within the autoclave kept air from enter- A is Selegted from the group consisting of in The samples were fabricated and tested using the E- same procedures as described in Example 3 except that H H the percent retention of the specific viscosity of the and samples was determined after 48 hours at 150C. The m results are reported below in Table III. N

TABLE III Performance of Phenolic Antioxidants and Sodium Hypophosphite in Autoclave Polymerized Nylon-6,6

R Antioxidant %NaH PO Time Stab! Form Stab. specific v i dosity (0.5%) Added Added After 48 hrs.

None None 2 0 1 None At start Aq. Disp. 36 l 0.l At start Aq. Disp. 62 0.1 After 3% hrs. 'Aq. Disp. 6| 1 0.1 After 5% hrs. Dry Powd. '128 2 0.! After 5% hrs. Dry Powd. 97

' Polymer was discharged from Autoclave at 6 hrs.

where m is a number from 2 to 8 and (C,,.H2m) is linear or cyclic, or

R and R are as defined aboveand Y is alkylene from 1 to carbon or of C H --SC H 2. The composition of matter of claim 1 wherein the metal hypophosphite is sodium hypophosphite or p0 tassium hypophosphite, wherein the concentration of said hypophosphite is in the range of about 0.05 to about 0.15 weight percent and the concentration of said phenolic antioxidant is in the range of about 0.05 to about 0.2 weight percent.

3. The composition of matter of claim 1 wherein the hindered phenolic compound is l,6-bi s[3(3,5-di-tbutyl-4hydroxyphenyl)propionamido]hexane.

4. The composition of matter of claim 1 wherein the hydroxy-S-t-butylphenyl)-propi0namido]ethane.

9. The compositions of matter of claim 1 wherein the hindered phenolic compound is N,N'-bis(3,5-di-tbutyl-4-hydroxybenzyl)adipamide.

10. The composition of matter of claim 1 wherein the hindered phenolic compound is ,bis[N-(3,5-di-t-butyl- 4-hydroxybenzyl)propionamide]sulfide. 

2. The composition of matter of claim 1 wherein the metal hypophosphite is sodium hypophosphite or potassium hypophosphite, wherein the concentration of said hypophosphite is in the range of about 0.05 to about 0.15 weight percent and the concentration of said phenolic antioxidant is in the range of about 0.05 to about 0.2 weight percent.
 3. The composition of matter of claim 1 wherein the hindered phenolic compound is 1,6-bis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionamido)hexane.
 4. The composition of matter of claim 1 wherein the hindered phenolic compound is 1,2-bis(3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionamido)ethane.
 5. The composition of matter of claim 1 wherein the hindered phenolic compound is 1,4-bis(3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionamidomethyl)cyclohexane.
 6. The composition of matter of claim 1 wherein the hindered phenolic compound is N,N''-bis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl)piperazine.
 7. The composition of matter of claim 1 wherein the hindered phenolic compound is 1,6-bis(3-(3-methyl-4-hydroxy-5-t-butylphenyl)-propionamido)hexane.
 8. The composition of matter of claim 1 wherein the hindered phenolic compound is 1,2-bis(3-methyl-4-hydroxy-5-t-butylphenyl)-propionamido)ethane.
 9. The compositions of matter of claim 1 wherein the hindered phenolic compound is N,N''-bis(3,5-di-t-butyl-4-hydroxybenzyl)adipamide.
 10. The composition of matter of claim 1 wherein the hindered phenolic compound is bis(N-(3,5-di-t-butyl-4-hydroxybenzyl)propionamide)sulfide. 